Aperson’s participation in a research project must be
random
rewarded
voluntary
public

answer; ///(c) i believe that the correct answer is ethnic relations bear many similarities across different global; good luck

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."

answer; the sound of a train whistle makes a woman think of an old friend; //

the smell of grass makes a by feel that spring is the best; (apex);

answer; (regions)